Hydrocarbon retorts for the most part reside beneath a surface layer of dirt and rock (and sometimes water as well). Thus, companies generally erect drilling rigs and drill piping from the surface to a point located below the surface to allow access and retrieval of the hydrocarbons from the retorts.
Drilling may comprise vertical wells, non-vertical wells, and combinations thereof. Vertical wells provide a reasonably straight drill path that is generally intended to be perpendicular to the earth's surface, and the drill bit is operational along the axis of the drill string to which it is attached. Non-vertical wells, also known as directional wells, usually involve directional drilling. Directionally drilling a well requires movement of the drill bit off the axis of the drill string. Generally, a directionally drilled wellbore includes a vertical section until a kickoff point where the wellbore deviates from vertical.
To directional drill, most operations use a motor steerable system or rotary steerable tool (sometimes referred to as RST or RSS). Both tools are useful because they allow for directional drilling (moving from vertical to horizontal in some cases), but also provide for a tool that generally travels in a straight path as well. A conventional RSS can generally be classified as a point the bit architecture or a push the bit architecture. A point the bit architecture generally flexes the shaft attached to the bit, to cause the bit to point in a different direction. The GEO-PILOT® rotary steerable system available from Halliburton Company is an exemplary point the bit architecture. A push the bit architecture generally has one or more pads on the outer surface of the rotating drill string housing. The pads press on the wellbore to cause the drill bit to move in the opposite direction causing a directional change in the wellbore. The AutoTrak Curve rotary steerable system, available from Baker Hughes Incorporated, is an exemplary push the bit architecture. Many companies offer steerable motors that incorporate a bent housing within its architecture that must be oriented in the desired position to generate the required directional change. The drill string that connects this assembly and bit to the rig floor must remain essentially stationary during the drilling of these directional change segments. Various RSS tool offerings have no non-rotational requirements or segments that need to be stationary while other RSS designs incorporate certain sections of the tool that must remain stationary or only rotate at a very slow speed.
FIG. 1, for background, shows a conventional steerable motor system 10 that is part of drill string 12 that extends from the surface, at the most proximal end 50, and terminates in drill bit 14 at distal end 52. Conventionally, as drill string 12 rotates as shown by arrow R and mud flow through steerable motor 16 adds rotation to bit 14, the steerable motor system drills in a generally straight line. The drilling path may be vertical or angled (generally between 0 to 90 degrees, but in some instances, up to 180 degrees with respect to vertical) depending on the drill plan. Once drill string 12 has deviated from vertical, a well bore direction is established and is typically measured, like a compass, as a magnetic heading or azimuth (ranging from 0 to 360 degrees). When steerable motor system 10 is being manipulated to directionally drill (by which directional or directionally drilling generally means modifying the angle of inclination and/or azimuth of the hole), where the rate of change is typically measured in degrees over a distance (generally degrees per 100 feet or degrees per 30 meters), rotation of drill string 12 from the surface is normally halted to facilitate directional change. As is well known in the art, one drawback of a conventional steerable system 10, is that cessation of rotation may cause friction to turn from dynamic to static resulting in an undesirable increase in friction between drill string 12, including steerable motor 16, and the wellbore (not shown).
In any event, drill string 12 includes a number of segments, not all of which are shown in FIG. 1, including drill piping or tubulars 26 to the surface, steerable motor 16 and drill bit 14. Steerable motor 16 generally comprises rotor catch assembly 18, power section 20, transmission 22, bearing package 24, and bit drive shaft 46 with bit box 34. Power section 20 generally comprises stator housing 28 connected to and part of drill string 12, and rotor 30. Transmission 22 includes transmission housing 36, that is part of drill string 12, and transmission driveline 38 that connects rotor 30 to bit drive shaft 46. Bearing package 24 includes bearing housing 42, part of the drill string, and one or more bearing assemblies 44 that may include different combinations of axial, radial, and thrust bearings. Transmission housing 36 generally includes bend 35 to modify drill bit 14 angular rotation axis B relative to drill string 12 rotation axis A, generally a bend is from around 0.5 to 5.0 degrees. (The modification of the angular axis of rotation is more thoroughly described below and is well-documented art.) Because the magnitude of bend 35 can be visually relatively small, the direction of the bend plane is generally marked by a shallow longitudinal groove called scribe line 40.
With mud flow, drilling mud (not shown) travels down internal cavities 32 of drill string 12 and through power section 20 causing rotor 30 to rotate with respect to stator housing 28 and therefore drill string 12. Rotor 30 drives rotation through transmission driveline 38 and bit drive shaft 46, to drill bit 14. Depending on the rotation direction (clockwise or counter clockwise) of rotor 30 relative to drill string 12, power section 20 can increase, decrease or reverse the relative rotation rate of drill bit 14 with respect to a rotating drill string 12. During drilling operations with a conventional steerable motor assembly 10, when it is determined to be desirable to modify the trajectory (angle of inclination and azimuth) of the wellbore, rotation of drill string 12 is terminated while maintaining mud flow through motor power section 20 and therefore continuing rotation of drill bit 14. By one of many methods that are well known and regularly practiced in the industry (such as MWD tools, LWD tools, drilling gyro tool and wireline orienting tool), the current orientation of drill bit 14 is determined. Drill string 12 is then manually oriented from the surface, generally by fractions of a full rotation, until scribe line 40 (and therefore bit 14) is oriented in the desired direction. Thus, the wellbore direction is altered in the direction of the scribe line 40 by the continued rotation of the drill bit 14 via the steerable motor 16 while the drill string 12 is not rotating. As the well continues to be drilled, the orientation of the scribe line 40 is continually monitored and adjusted to create the desired wellbore path. The adjustment of the scribe line 40 conventionally includes manual orientation of the drill string to keep the scribe line 40 oriented in the desired direction. The details of conventional steerable motor system 10 are reasonably well known in the industry and will not be further explained except as necessary to understand the technology of the present application.
Drill bit 14 conventionally can be a number of different styles or types of drill bits. Drill bit 14 may be a polycrystalline diamond cutter (PDC) design, a roller cone (RC) design, an impregnated diamond design, a natural diamond cutter (NDC) design, a thermally stable polycrystalline (TSP) design, a carbide blade/pick design, a hammer bit (a.k.a. percussion bits) design, etc. Each of these different rock destruction mechanisms has qualities that make it a desirable choice depending on formation to be drilled and available energy in association with the drilling apparatus.
For a variety of disparate reasons, drill bit technology integrated within a drilling apparatus or drilling machine methodology could use much improvement, whether implemented in a vertical drilling system or incorporated into a Steerable Motor or RSS usable with directional drilling. Thus, against the above background, improved drill bits separately or as part of an integrated drilling apparatus or machine coordinated with drill string components, are further described herein.